In a TV system, one function of the tuner is to select a signal of a desired channel from a received broadband television (TV) signal, and perform subsequent signal processing on the selected signal of the desired channel. A conventional CAN tuner has a large volume. In addition, the tuner implements a trace filter with a capacitive/inductive filter as to select a desired frequency, with a capacitor of the trace filter being a varactor. However, since a broadband TV signal (i.e., the TV signal having a large frequency range) is to be processed by the tuner, the varactor correspondingly needs a large variable range, i.e., a high supply voltage (about 30 V) for driving the varactor.
A silicon tuner is developed to overcome the foregoing disadvantages of a CAN tuner with a large volume and a high supply voltage requirement for a varactor. Although a silicon tuner has advantages in having a small volume and a lower supply voltage requirement (about 3 V), transconductance values of components and noises need to be taken into consideration for that a trace filter of the silicon tuner, which is realized by an active device. Therefore, the silicon tuner needs to be produced by a bipolar junction transistor (BJT) manufacturing process. Yet, a silicon tuner manufactured by the BJT manufacturing process has a rather large area, and a production cost of the silicon tuner cannot be reduced since the BJT manufacturing process is more costly.
Furthermore, a conventional tuner has three front-end filter circuits, i.e., a low-pass filter circuit, a band-pass filter circuit, and a high-pass filter circuit. Due to the cost considerations, the three front-end circuits are implemented in one single chip by capacitors and inductors. As a result, the cost is reduced by the sacrifice of the filtering quality.